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. Author manuscript; available in PMC: 2009 Aug 5.
Published in final edited form as: Biochemistry. 2008 Jul 11;47(31):8058–8069. doi: 10.1021/bi800443k

Figure 2. Trends in Kd and allosteric response for LLhP variants binding to alternative lac operators.

Figure 2

The symbols and colors in legend shown are used for all three panels. For panel (A), “+” indicates the presence of saturating hypoxanthine. (A) Affinities of LacI and LLhP variants for lacO1, lacOsym, and lacOdisC. LacI (dashed black line) shows steeper discrimination between the 3 operators than does LLhP (solid black line). With the exception of LLhP+HX+lacOsym, unmodified LLhP, the 48 variants, and the 55 variants have different affinities but the same selectivities (solid, parallel lines). The LLhP variants at position 61 show a different pattern of DNA selectivity (dotted lines). (B) Allosteric ratios of LLhP variants report the magnitude of change in Kd when the repressor binds hypoxanthine. Data for S61C and S61M are slightly offset to aid visual inspection. (C) Midpoints of operator capture for LLhP variants reflect the amount of hypoxanthine required to elicit the full allosteric change.